Intensification of Consonants in English Pronunciation

In many languages, my mother tongue included, you frequently encounter words that have an intensified consonant within them, especially if the consonant is between two vowels.

A good idea to demonstrate how intensification of a sound works, is to repeat the respective phonetic symbol, ie: to write it twice. For example, teammate can be pronounced /tēmmāt/, with an intensified /m/. Sometimes, in informal writing, a letter is typed repeatedly to imply intensification: "What the ****** ^{(with three f's)}are you doing?"

What I've recently noticed is that intensification is not used in English as much as in the other languages I know (about). Particularly, seldom is a sound naturally intensified inside a word. To be clear, these are (some of?) the occasions where I've come across intensification in English:

• when two words meet, the first ending in the sound that the second begins with: hot tub, teammate.
• when two words meet, the first ending in the sound similar to the one that the second begins with: hot chocolate (with intensified /tʃ/).
• when emphasizing a word: This is absolutely unacceptable (with intensified /l/), She's my (bbb)best friend (with intensified /b/).

But almost never inside a word.

My questions:
1- Are there any words in English that have internal intensification?
2- If the answer to the above is negative, then can we ask why? ?
3- Was it like this, say, in Old English? Maybe intensification was a common feature of English, but got gradually worn away?

Perhaps it doesn't seem an important issue, but it strikes me as very odd, because intensification is such a naturally and statistically probable thing to happen. Suppose we are to construct words by choosing sounds and chaining them together, abiding by the human limitations of articulation. After a consonant /x/, one of the nearest, and thus most probable consonant sounds to come is /x/ itself, isn't it?

EDIT:
In phonetics, a sequence of two identical sounds is called a geminate. "Intensification" might be misleading, because it also implies a change in the pitch and/or volume of the voice, which don't necessarily happen when geminating a sound.

Solution 1:

Regarding the history, Old English did have contrastive consonant length, although long consonants were not as common as single ones and were more restricted in position (they could not come at the start of a word, for example). This is related in fact to the use of "double" consonants to indicate vowel quality in the modern English writing system. (This is not to say that all double consonants in modern spelling correspond to Old English long/geminate consonants!) The contrast between long and short consonants was later lost as an overall feature, but several other contrasts that it contributed to remained.

For example:

• Vowels ended up being lengthened in some positions before single consonants, while they remained short before geminate consonants. Later on, contrastive vowel length was also lost as a phonological feature of English, but it is often reflected in Modern English contrasts in vowel quality. (Apparently, the term for this is "transphonologization," found in the answer to this question: What did we gain in return for the loss of phonemic vowel length from Old English?) Examples: Old English eall/all is cognate to Modern English all /ɔːl/; Old English talu is cognate to Modern English tale /teɪl/
• Geminate fricatives such as [ff, ss] were always voiceless, while single fricatives were voiced [v, z] in some circumstances, such as between vowels. This voicing is generally not considered to have been contrastive in Old English, but it has become contrastive in Modern English. (For a more detailed explanation, see this paper: An explanation for the early phonemicisation of a voice contrast in English fricatives.) Examples: Old English ofer and dysig are cognate to Modern English over and dizzy; Old English offrian and cyssan are cognate to Modern English offer and kiss. There were not actually that many words with /ff/ in Old English, though, and even fewer survived to Modern English; it took me a bit of time to find these examples.
• Geminate /jj/ was apparently realized as an affricate [dː͡ʒ] in Old English; this affricate continued to contrast with /j/ even after the lost of contrastive consonant length. In Modern English, this is reflected as a contrast between words with /d͡ʒ/ and words with a front vowel or diphthong ending in a front vowel component. Examples: Old English hegg/hecg is cognate to Modern English hedge /hɛd͡ʒ/; Old English weg is cognate to modern English way /weɪ/
• Geminate /gg/ developed into /g/; single /g/ developed into /w/ when at the end of a syllable or between vowels (it was realized as a fricative or approximant [ɣ], or at the end of a word [x], in these positions in Old English). In Modern English, this is reflected as a contrast between words with /g/ and words with a back vowel or diphthong ending in a back vowel component. Examples: Old English frogga/frocga is cognate to Modern English frog /frɒg/ (in some North American varieties, /frɔːg/); Old English boga is cognate to Modern English bow /boʊ/ (as in "bow and arrow")

Many of these changes are shared to some degree by other languages nearby:

• German also had vowel-lengthening in certain contexts before single consonants but not before geminate consonants, and developed a contrast between voiceless geminate /ss/ and voiced single /z/ that became a pure voicing contrast /s/ vs. /z/ when geminates were simplified. (There are a number of German dialects/related languages that still have length contrasts for consonants, but standard German does not.)
• Western Romance languages historically have a voicing contrast of /f, s/ vs. /v, z/ that dates back in part to an original, lost length contrast /ff, ss/ vs. /f, s/. This voicing contrast is still visible in Modern French, which only has type 1 and type 3 gemination (using Greg Lee's terminology). French loanwords are thought to have influenced the development of the English voicing contrast in fricatives.

Solution 2:

There are arguably 3 different phenomena involved in your examples, and your term "intensification" is appropriate for the one you say is due to emphasis. The other two are not affective (like emphasis, type 3), but are due to consonants having a length attribute, type 2, (as some languages, like Latin, have long vowels), or clusters of two like consonants, type 1. I've numbered these types just for convenience of reference -- the numbers are not standard. A standard term which refers to either type 1 or type 2 is "gemination" (see Tim Romano's comment above).

English has type 3, affective lengthening, as you note, and type 1 gemination across word boundaries. It does not have type 1 gemination within a morpheme; perhaps it is possible across morpheme boundaries in words like "unknown" or "coolly". English does not have type 2 gemination.

Finnish has type 2 gemination, which is phonologically important, because it is regular for long consonants to lose their length at the beginning of a closed syllable.

Estonian has 3 degrees of consonant length, short, long, and over-long, which might represent a combination of types 1 and 2 length.

The phonological relationship between types 1 and 2 is discussed in this article by Pyle and Kenstowicz: On the phonological integrity of geminate clusters.